Photographic emulsion.



YORK SCEZXVrlBTZ, 0E HANOVER, GERMANY.

lEtBTOG-BAPHIC EMULSION l'ti fl idr N0 Drawing.

To all whom it may concern:

Be it known that I, YORK SCHWARTZ, a subject of the King of Prussia, and resident of 3 Edenstrasse, Hanover, in the German Empire, have invented a new and useful Photographic Emulsion, of which the following is an exact specification.

The present invention relates to an improved photographic emulsion of the kind set forth in the specification of United States patent granted to York Schwartz No. 710019 dated September th, 1902. I The emulsion is there indicated as containing an emulsifying agent, silver phosphate, silver chlorate and a silver salt o1 an organic acid. It has been found that such an emulsion is insuiliciently sensitive for some purposes and accordingly the present invention has for its object to modify the emulsion in such a manner as to obtain greatly increased sensitiveness. l or this purpose in the improved form of the emulsion the proportion of the phosphate used is increased so that it is considerably in excess of that theoretically necessary for the decomposition of the whole of the silver nitrate employed in the preparation of the emulsion.

The preparation of the emulsion is carried out as tollo\vs:-ln the presence of a colloidal substance, for instance gelatin, an alkaline phosphate, pre 'erably disodium phosphate, is mixed with nitrate of silver, the relative proportion of the phosphate being as above indicated in excess of that necessary for the decomposition of the silver nitrate. It has been round in practice that it is preterable to use double the quantity of phosphate which would ordinarily be necessary to etlect this decomposition. To this mixture an oxidizing agent, such as chlorate of potassium, and citric acid or its equivalent are added and if desirable a small quantity of chrome alum may be used for rendering the sensitive surface more resistant.

It is at present impossible to state with certainty what chemi al action the various constituents of the mixture have upon one another in forming the emulsion. The chlorate of potassium acts as an oxidizing agent, and the citric acid acts as a solvent for the phosphate, without decomposing the same, as is clearly well known. There is also no doubt that the whole of the silver nitrate is decomposed by the phosphate. The exact nature of theiaction of the other constituents of the mixture is however not so clearly un- Speoification of Letters Patent. Patentqgfl June 28, 191M), Application filed May 6, 1907. Serial No. 372,232.

derstood. In ordinary course if citric acid were brought in contact with the alkaline phosphate the phosphate would be decomposed and a citrate and freephosphoricacid produced. The special conditions of the present case however appear to bring about a further reactiori and, although the inventor has hitherto been unable to prove the theory by isolating and analyzing the compound, he has good reasons for believing that a double salt of the form of a phospho-citrate of silver is produced. This compound when acted upon by the developer after the action of light has loosened the cohesionof its constituents appears to be split up into two compounds, one of which during development liberates nascent silver while the other attracts this body, the-extent of these actions being proportional to the light action to which each part of the sensitive surface has been subjected. The applicant does not however bind himself to this explanation of the constitution of the emulsion.

Experiments have proved the-emulsion to be sutticiently sensitive to enable to be used not only for contact-printing, but also for enlarging purposes and tiveprocess. While in the former cases the development is carried out physically i. e. in acid or neutral solution, chemical developnient, i. 3. in alkaline solution, is preferably used in the latter. Every sort of suitable material, paper, glass, etc, may be coated with the emulsion.

The best develo or for this emulsion isa simple aqueous solution of metol. velopers necessary for the development of the emulsion prepared according to the patent above referred to were of rather complicatcd nature and are entirely dispensed with in the case of the new emulsion.

The pictures developed by means of the aqueous motel-solution show great intensity and brilliancy and very nice tones, and furtherinore great durability. By adding 'sullite of sodium to the aqueous solution at inetol the rapidity of development is so increased that it takes place nearlyinstanta- 'neously, the development in this case being a chemical one. This method of develgpment is preferably used for the negative process with this emulsion.

Claims.

1. A. photographic emulsion formed by the mixture, with a ctdloidal substance and silver nitrate, of a quantity of alkaline phoseven for the nega- The de- Ver nitrate,

phate in considerable excess of that required to decompose the whole of the silver nltrate, with an oxidizing agent and a substance acting as a solvent for the phosphate without decomposing the same.

2. A photographic emulsion formed by the mixture with a colloidal substance and silver nitrate, of a quantity or" alkaline phosphate approximately double that required for the decomposition of the whole of the sil- With an oxidizing agent and a substance acting as a solvent for the phosphate without decomposing the same.

3. A photographic emulsion formed by the mixture with a colloidal substance and 15 silver nitrate, of a quantity of disodium phosphate approximately double that required for the decomposition of the whole of the silver nitrate, with chlorate of potassium and citric produced having as one of its principal constituents a phospho-citratecompound.

In witness whereof I have hereunto. set my hand in the presence of two witnesses. YORK SCHWARTZ. Witnesses:

PAUL R. THOMPSON, ,H. T. FULLER.

acid, whereby an emulsion is 20 

